Conventionally, there have been optical semiconductor devices including an optical semiconductor element capable of emitting light having a prescribed wavelength. As such an optical semiconductor device, for example, an optical semiconductor device B shown in FIG. 5 is known. This optical semiconductor device B is configured of a lead frame 33 composed of a first plate part 31 and a second plate part 32, which is disposed on the bottom thereof; an optical semiconductor element (not shown) and the like placed on the second plate 32; a circumferential reflector 34 formed on the lead frame 33 so as to surround the optical semiconductor element; and a transparent resin 36 for encapsulating the inside of a recess 35 configured of the lead frame 33 and the reflector 34. Incidentally, FIG. 6 shows a state of the semiconductor device B seen from the rear surface side.
In order to enhance the manufacturing efficiency, for example, as shown in FIG. 7, in order that a large number of optical semiconductor devices may be produced at once, such an optical semiconductor device B is manufactured using a lead frame forming plate 37 having a large number of the lead frames 33 formed in continuity. That is, the optical semiconductor device B is manufactured by first arranging a large number of optical semiconductor elements in a line and mounting them on one sheet of the lead frame forming plate 37 to manufacture a large number of optical semiconductor devices at the same time and then cutting off the respective optical semiconductor devices and individualizing them from each other. In manufacturing the foregoing optical semiconductor device, the circumferential reflector 34 is formed in the lead frame forming plate 37 by resin molding, and examples of this resin molding include transfer molding. According to this method, as shown in FIG. 8, the reflector 34 can be formed by interposing the lead frame forming plate 37 into a molding die configured of an upper die 38 and a lower die 39 and performing clamping to form a cavity part 40, injecting a molten resin into the inside of this cavity part 40, and curing the injected resin, followed by demolding (see, for example, Patent Document 1). Incidentally, in FIG. 8, 41 is a side gate for injecting a molten resin, and 42 is an air vent for discharging internal air following the injection of a molten resin.
At that time, in order to produce a larger amount of the lead frames 33 from one sheet of the lead frame forming plate 37, the contour shape of the individual lead frame 33 is generally made in an approximate rectangle. On the other hand, since the reflector 34 is one for reflecting the light emitted from the optical semiconductor element toward the upper direction, it is formed in a circumferential state of surrounding the optical semiconductor element, and the contour shape of the bottom of the recess 35 formed by the lead frame 33 and the inner periphery of the reflector 34 is made in a form of an approximate circle or approximate oval (see FIG. 5).
Accordingly, at the time of transfer molding, there is likely caused such a problem that in the lead frame 33 located in the inside of the cavity part 40, the molten resin comes into a space between the lead frame 33 and the lower die 39 from the four corners thereof, whereby an unnecessary matter called a resin burr is formed on the rear surface of the lead frame 33. That is, in the lead frame 33, as shown in FIG. 9, at the time of clamping the upper and lower dies 38 and 39, though only a portion 43 with which the upper die 38 comes into contact is firmly interposed between the upper die 38 and the lower die 39, other portion does not come into contact with the upper die 38, so that an upper part thereof becomes in a free state. Accordingly, the molten resin comes into the space between the lower die 39 and the lead frame 33 from the four corners of the lead frame 33 located far from the portion 43 with which the upper die 38 comes into contact, whereby the resin burr is formed on the rear surface of the lead frame 33. At the time of performing electric mounting such as solder joint, e.g., IR reflow, the resin burr causes the repulsion of solder or the like, resulting in joint failure, and therefore, a step of removing this becomes necessary. Incidentally, the lower die 39 is seen from the through-holes of the lead frame forming plate 37.
In order to solve such a problem, in the field of molding a QFN (quad flat non-leaded) package, there is also adopted a technique of previously covering the rear surface of the lead frame 33 by an exclusive release tape prior to performing resin molding and removing a resin burr formed after the resin molding together with the release tape (see, for example, Patent Document 2).
Patent Document 1: JP-A-2008-218964
Patent Document 2: Japanese Patent No. 3934041